1. Field of the Invention
The present invention relates to organic phosphite ester compositions, and more particularly relates to organic phosphite ester compositions hydrolytically stabilized by a hindered piperidinyl light stabilizer.
2. Description of the Related Art
The purpose of stabilizers for polymers is to prevent deterioration of the polymers during processing at high temperatures, and also to permit manufacture of products with increased intrinsic quality because of the enhancement of their resistance to thermal and light degradation during use. In addition, because of the ability of these products to withstand more rigorous conditions, their versatility is increased and new areas of application are thereby opened.
An important class of polymer stabilizers are the organic phosphites. They include, as a specially useful group, the dialkylpentaerythritol diphosphites and diarylpentaerythritol diphosphites. They are used widely in the stabilization of vinyl chloride polymers, polyolefins and styrene polymers such as ABS. The dialkylpentaerythritol diphosphites and diarylpentaerythritol diphosphites have the structural formula: ##STR1## where each R is independently selected from alykyl or aryl groups.
Despite such wide usage, however, these types of stabilizers have not been entirely satisfactory, because of their own slight hydrolytic instability on storage. They tend to absorb moisture from a moist environment and their effectiveness as stabilizers for polymers seems to decline in direct proportion to the amount of water absorbed.
This disadvantage can be avoided by taking care to store and transport the stabilizer only in a dry atmosphere. Once incorporated in a polymer composition, lesser problems are presented apparently because of the essentially anhydrous condition of such polymer compositions.
Obviously, though, elimination or a least amelioration of the problem is desirable. A moisture-insensitive phosphite stabilizer will preclude the many inconveniences and expense associated with having to maintain an anhydrous environment, prior to incorporation into polymer.
U.S. Pat. No. 3,553,298 (Hodan) shows the stabilization of phosphite esters broadly by using any of several classes of amines including triisopropanol amine. See column 2, line 24 and Examples I-VI.
M. C. Imaev, Zhurnal Obshchel Khim. 31, 1767-70 (1961) shows the stabilization of lower trialkyl phosphites with organic and inorganic bases. The organic bases shown include pyridine, triethyl amine and dimethyl aniline.
U.S. Pat. No. 2,114,866 (Vaughn) shows the stabilization of esters of inorganic esters with an amine. While Vaughn is interested primarily in organic silicates he does mention also (see page 2, column 2, lines 17-22) borates, phosphates, "symmetrical" phosphites, arsenates and symmetrical arsenites.
U.S. Pat. No. 3,787,537 (Marcq) discloses a class of phosphite esters which are said to be stable to hydrolysis. Marcq refers also (see column 2, lines 9-10) to the stabilization of previously known phosphites by "a small quantity of a heavy amine, usually triisopropanolamine (French Pat. No. 1,582,387)". The cited French patent is a counterpart of the above Hodan et al U.S. patent.
As mentioned above, ultraviolet light has a degradative effect on olefin polymers, the severity of which is dependent on the particular polymer and the geographical location of exposure. The degradation may take the form of discoloration, loss of tensile and impact strength, distortion of initial flexibility, dimensional change, surface craze, cracking, powdering or increased electrical conductivity. All of these effects may result from the breaking of carbon-to-carbon bonds in the polymer or from crosslinking of the polymer.
It is well known that the addition of certain materials to an olefin polymer will impart a degree of stabilization to that polymer with respect to its resistance to the destructive forces of ultraviolet radiation. Hindered amine light stabilizers are commonly used in many polymers to inhibit polymer degradation which is accelerated by exposure of the polymer to light.
U.S. Pat. No. 3,640,928 (Murayama et al.) which is incorporated herein by reference shows the stabilization of synthetic polymers by the presence therein of certain piperidine compounds wherein the two carbon atoms adjacent to the ring nitrogen each contain two alkyl substituents. The piperidine compounds contain also an oxy substituent in the four-position and, in many instances, two or more piperidine nuclei are joined to one another by means of polyfunctional ether, ester, carbamate, sulfonate, etc. groups.
U.S. Pat. No. 4,302,383 (Valdiserri et.al.) which is incorporated herein by reference shows the stabilization of olefin polymer compositions containing stabilizer composition comprising a cyclic hindered amine selected from pyrrolidines and pyrrolines in combination with an organic phosphite ester.
While both phosphites and hindered amines are known additives for stabilizing polymeric compositions, applicant has discovered that combining these phosphite antioxidants and hindered piperidinyl light stabilizers as a nonpolymeric blend composition provides an organic phosphite ester composition that contains a light stabilizer that hydrolytically stabilizes the phosphite ester antioxidant contained therein.